1. Field of the Invention
The present invention relates to a vacuum heat treatment furnace, and more particularly to a vacuum heat treatment furnace structured such as to prevent a deterioration due to a carburizing and increase an efficiency of thermal energy with respect to a subject or a work to be treated in a vacuum heat treatment, a vacuum carburizing treatment and the like, and a method of and apparatus for measuring a carbon concentration in an atmosphere having a reduced pressure.
2. Description of the Prior Art
A method of carburizing an iron and steel material under a reduced pressure conventionally includes a vacuum carburizing method carried out by introducing a hydrocarbon series gas within a furnace, in which a carbon material is frequently employed for a heat insulating material and a heater as furnace constituting members, and a heat resisting steel, a heat resisting cast steel, a carbon series material or the like is employed for a hearth rail for supporting the subject to be treated and a hearth roller for transferring. Further, the vacuum heat treatment furnace has a type in which a furnace wall is water cooled and a type in which the furnace wall is not water cooled by making the heat insulating material thick so as to increase a heat insulating property, in view of a working environment and the heat insulating property.
However, in the case that the iron series material (a hard carburized material: containing a high Ni high Cr material) is used for the furnace constituting material in a high temperature range, the furnace constituting material is also carburized at the same time when the subject to be treated is carburized, in the vacuum carburizing treatment, so that there is a case that the material becomes brittle and is broken. Further, even in the case of making the heat insulating material thick without water cooling the furnace wall so as to increase the heat insulating property and reduce an amount of heat radiation, for the purpose of reducing the thermal energy, a large amount of heat reserve of the heat insulating material is required, so that the thermal energy required for increasing the temperature is increased and a lot of time is also required for reducing the temperature.
Further, as a means for directly measuring a carburizing within a heat treatment furnace or a carbon concentration of an anti-oxidized atmosphere, a steel wire method is shown, for example, in Japanese Patent Publication No. 45-35411. Further, with respect to a holding rod for holding the steel wire for measuring the carbon concentration, for example, there is a structure shown in Japanese Utility Model No. 2586972.
However, the measurement in accordance with the steel wire method is carried out by inserting the steel wire for measuring the carbon concentration into an atmosphere normally equal to or more than an atmospheric pressure, and it is hard to insert the steel wire for measuring the carbon concentration in the atmosphere having the reduced pressure. Further, the vacuum carburizing under the reduced pressure corresponds to a treatment in which a carbon is directly carburized into the steel, and it is not carried out to control and measure the carbon concentration in the atmosphere within the furnace.
The present invention solves the problems mentioned above.
An object of the present invention is to provide a vacuum heat treatment furnace comprising a furnace shell, a casing arranged in an inner side of the furnace shell, a heat insulating layer consisting of a thick plate-like alumina-silica series ceramic fiber blanket and a thin plate-like alumina series ceramic material arranged in an inside of the casing, and a heater arranged in a heating room surrounded by the heat insulating layer.
Another object of the present invention is to provide a vacuum heat treatment furnace comprising a furnace shell, a casing arranged in an inner side of the furnace shell, a heat insulating layer consisting of a thick plate-like alumina-silica series ceramic fiber blanket of multilayer and a thin plate-like alumina series ceramic material arranged in an inside of the casing, and a heater arranged in a heating room surrounded by the heat insulating layer.
A further object of the present invention is to provide the vacuum heat treatment furnace, wherein at least one layer in the ceramic fiber blanket of multilayer consists of a board, felt or plate of carbon fiber.
Still further object of the present invention is to provide the vacuum heat treatment furnace, further comprises a fan formed of a high strength carbon fiber for circulating by convection gas atmosphere, arranged in the heating room surrounded by the heat insulating layer.
Yet further object of the present invention is to provide the vacuum heat treatment furnace, further comprises a roller for transferring a subject to be treated, and a tray guide which is easy to replace and prevents the surface of the roller from being damaged, both of the roller and the tray guide being arranged in the heating room surrounded by the heat insulating layer.
Yet still further object of the present invention is to provide the vacuum heat treatment furnace, further comprises a work position detecting flapper arranged in the heating room surrounded by the heat insulating layer.
A further object of the present invention is to provide an apparatus for measuring a carbon concentration in an atmosphere having a reduced pressure comprising a carbon concentration measuring body insertion port communicating between an external portion of a furnace shell of a heat treatment furnace and a treating room within the furnace shell, means for exhausting an internal portion of the port, means for maintaining a vacuum seal of a portion of the port outside of the furnace shell, means for transferring a carbon concentration measuring body from the external portion of the furnace shell into the treating room, and means for measuring an amount of carbon in the carbon concentration measuring body.
Yet further object of the present invention is to provide the apparatus for measuring a carbon concentration, wherein means for maintaining the vacuum seal of the portion of the port outside of the furnace shell is means for fastening and holding the carbon concentration measuring body transferring means.
Still further object of the present invention is to provide a method of measuring a carbon concentration in an atmosphere having a reduced pressure comprising the steps of exhausting an internal portion of a carbon concentration measuring body insertion port communicating between an external portion of a furnace shell of a heat treatment furnace and a treating room within the furnace shell, transferring a carbon concentration measuring body from a portion of the port outside of the furnace shell into the treating room, reacting the carbon concentration measuring body with the atmosphere in the treating room for a predetermined time, gradually cooling the carbon concentration measuring body for a predetermined time, drawing out the carbon concentration measuring body to the portion of the port outside of the furnace shell, cooling the carbon concentration measuring body to a room temperature, and measuring an amount of carbon in the carbon concentration measuring body in the atmospheric pressure.
Yet still further object of the present invention is to provide the apparatus for measuring a carbon concentration, wherein the carbon concentration measuring body is a carbon concentration measuring steel wire, a carbon concentration measuring steel foil or a test piece of a subject to be carburized.
The forgoing and other objects, features, and advantages of the present invention will become apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.